1. Field of the Invention
The present invention relates to a polymerization process giving superior reaction results such as initiation efficiency, comprising an anionic polymerization of a methacrylic ester or an acrylic ester in the presence of a specific organoaluminum compound, using a specific polymerization initiator compound. The present invention also relates to a process for producing a polymer such as a block copolymer, wherein the above-mentioned polymerization process is used.
2. Related Art of the Invention
Not only realization of high living polymerization property but also an improvement in initiation efficiency are important for anionic polymerization. The improvement in the initiation efficiency is especially important for synthesis of a block copolymer as well as enhancement of use efficiency of a polymerization initiator compound. For example, the following process is assumed: a process for synthesizing a block copolymer comprising a polymer block resulting from a certain kind of monomer (hereinafter referred to as a first monomer) and another polymer block resulting from another kind of monomer (hereinafter referred to as a second monomer), comprising polymerizing the first monomer to synthesize a living polymer, and then polymerizing the second monomer by use of the living monomer as a polymerization initiator compound. If the initiation efficiency of the living polymer (block efficiency in this case) is low, a product which is actually obtained is a mixture of the block copolymer and a polymer resulting from the first monomer. In many cases, the above-mentioned impurity produced by interruption of the polymerization causes a remarkable drop in performances of the block copolymer. It is known that, for example, a triblock copolymer having a structure of a hard block/a soft block/a hard block has properties as a thermoplastic elastomer. If a polymer having only a hard block or a diblock copolymer having a structure of a hard block/a soft block is mixed with this type triblock copolymer, mechanical properties such as tensile strength drop. Block copolymers are frequently used as compatibilizer for different resins. However, if a homopolymer is mixed with a used block copolymer, the function as the compatibilizer deteriorates so that good points which respective resins originally have in a resultant resin composition are not sufficiently exhibited.
As a process for heightening initiation efficiency in anionic polymerization of a methacrylic ester or an acrylic ester, there is known a process comprising the steps of subjecting an organic alkali metal compound, for example, an alkyl lithium such as butyllithium, or a lithiated polymer such as polystyryllithium to addition reaction with 1,1-diphenylethylene or xcex1-methylstyrene to prepare a compound having, at its terminal site, a diphenylmethylene anion structure or a phenylmethylene anion structure; and then polymerizing a methacrylic ester anionically in a solvent comprising tetrahydrofuran alone or a mixture of tetrahydrofuran and toluene at a low temperature, for example, xe2x88x9260xc2x0 C. or lower, using the above-mentioned compound as a polymerization initiator compound (Macromolecules, Vol. 23, pp. 2618-2622 (1990)). A polar solvent, such as tetrahydrofuran used in this process, is easily mixed in waste water at the time of washing with water after the polymerization, and further is not easily separated from the waste water. Therefore, the polar solvent is not suitable for industrial use. As a result, in order to carry out industrially anionic polymerization in a solution of a methacrylic ester or an acrylic ester, it is desired to use a nonpolar solvent, such as a hydrocarbon based solvent, as a solvent.
As a process for making it possible to polymerize a methacrylic ester or an acrylic ester anionically in a hydrocarbon based solvent, a process wherein an organoaluminum compound causes to be present in the polymerization system is suggested. It is considered that in this case, the organoaluminum compound has a function of lowering nucleophilicity of the growing terminal of the polymer and stabilizing the growing terminal by coordination, as a Lewis acid, to a used polymerization initiator compound or the growing terminal of the living polymer in the middle of the polymerization. Examples of reports on such a polymerization process are as follows.
(1) Anionic polymerization of a methacrylic ester using tert-butyllithium was conducted in the presence of an organoaluminum compound such as a trialkylaluminum or a dialkyl(diphenylamino)aluminum in toluene at xe2x88x9278xc2x0 C. to obtain a methacrylic ester polymer having a narrow molecular weight distribution (JP-B-H7-57766).
(2) Anionic polymerization of a methacrylic ester using an organolithium compound such as tert-butyllithium was conducted in the presence of a specific organoaluminum compound having one or more bulky groups (for example, triisobutylaluminum or diisobutyl(2,6-di-tert-butyl-4-methylphenoxy) aluminum) in a hydrocarbon solvent at a temperature of about xe2x88x9210xc2x0 C., which is a relatively mild cooling condition (U.S. Pat. No. 5,180,799).
(3) Anionic polymerization of a methacrylic ester or an acrylic ester using tert-butyllithium was conducted in the presence of methylbis(2,6-di-tert-butylphenoxy)aluminum or ethylbis(2,6-di-tert-butylphenoxy)aluminum in toluene at a temperature of xe2x88x9260xc2x0 C. or xe2x88x9270xc2x0 C. to obtain a homopolymer or a block copolymer having a narrow molecular weight distribution (Polymer Preprints, Japan, Vol. 46, No. 7, pp. 1081-1082 (1997) and Vol. 47, No. 2, p.179 (1998)).
(4) An organolithium compound such as tert-butyllithium, sec-butyllithium, ethyl xcex1-lithioisobutyrate, 1,1-diphenylhexyllithium was mixed with an organoaluminum compound such as methylbis(2,6-di-tert-butylphenoxy)aluminum, ethylbis(2,6-di-tert-butylphenoxy)aluminum or tris(2,6-di-tert-butylphenoxy)aluminum, and then the mixture was brought into contact with methyl methacrylate to anionically polymerize methyl methacrylate in a nonpolar organic solvent such as toluene at about room temperature. In this way, an initiation efficiency of 0.05-0.63 was attained (U.S. Pat. No. 5,656,704).
(5) Anionic polymerization of a methacrylic ester or an acrylic ester using an organolithium compound such as methyl xcex1-lithioisobutyrate or tert-butyllithium was conducted in the presence of an organoaluminum compound, such as a trialkylaluminum, and an ester compound, an ether compound or an organic quaternary salt in a hydrocarbon based solvent such as toluene at a temperature of about xe2x88x9280xc2x0 C. to 0xc2x0 C., so as to obtain a polymer having a narrow molecular weight distribution (Macromolecules, Vol. 31, pp. 573-577 (1998) and International Publication WO98/23651).
(6) An organolithium compound such as n-butyllithium was subjected to addition-reaction with butadiene to prepare polybutadienyllithium, and then the polybutadienyllithium was reacted with tert-butyl methacrylate in the presence of a trialkylaluminum such as triethylaluminum at 50xc2x0 C., so as to obtain a block copolymer (U.S. Pat. No. 5,514,753).
According to the above-mentioned processes (1)-(6), anionic polymerization of a methacrylic ester or an acrylic ester can be attained in a hydrocarbon based solvent. However, in order to use these processes as industrial polymerization processes, they have the following points to be further improved.
The polymerization initiator compound used to polymerize a methacrylic ester or an acrylic ester in specific polymerization examples in the above-mentioned (1)-(3) processes is limited to tert-butyllithium. It can be presumed that in order to attain good polymerization results in these polymerization examples, it is preferred to use tert-butyllithium. However, tert-butyllithium has intense self-ignition ability. Thus, if tert-butyllithium is industrially used, problems about safety and handling performances thereof upon transportation and storage thereof arise.
In the processes (1) and (3), the polymerization temperatures used in specific polymerization examples therein are very low temperatures, such as about xe2x88x9280 to xe2x88x9260xc2x0 C. It can be presumed that in order to attain good polymerization results in these polymerization processes, it is preferred to use very low temperatures as described above. However, many utilities are necessary for cooling to such temperatures; therefore, the processes are industrially disadvantageous.
In the process (4), almost all of the initiation efficiencies in specific polymerization examples of methyl methacrylate are 0.5 or less even in examples wherein tert-butyllithium, which can give relatively good polymerization results, is used as a polymerization initiator compound. In an example wherein sec-butyllithium, which is a polymerization initiator compound that is relatively good in handling performance, is used, the initiation efficiency thereof is 0.17. Thus, the initiation efficiencies are on an insufficient level.
The polymerization initiator compounds used in specific examples in the process (5) are limited to tert-butyllithium and ethyl xcex1-lithioisobutyrate. It can be presumed that in order to attain good polymerization results, it is preferred to use these polymerization initiator compounds. As described above, tert-butyllithium has problems for industrial use from the standpoint of safety and handling performance. Synthesis operation for producing ethyl xcex1-lithioisobutyrate and subsequent purification operation are complicated. Therefore, it is difficult to say that ethyl xcex1-lithioisobutyrate is suitable for industrial use.
The inventor et al. tried to reproduce the process (6) experimentally, but could not obtain desired results. That is, the inventor et al. prepared specified polybutadienyllithium on the basis of the specific production examples described as the process (6), and then reacted the polybutadienyllithium with tert-butyl methacrylate in the presence of triethylaluminum at 50xc2x0 C., but the initiation efficiency of the polybutadienyllithium was low in the present polymerization system. A finally obtained product was a mixture of a block copolymer and polybutadiene. Accordingly, the process (6) has problems when this process is adopted for industrial production for which high reproducibility is required.
Furthermore, the inventor et al. made experimental investigations on the processes (1)-(6). As a result, it was proved that polymerization of esters of a primary alcohol and methacrylic acid or acrylic acid, such as methyl methacrylate and n-butyl acrylate, does not advance in many cases, or that even if polymerization reaction thereof advances, reaction results such as initiation efficiency and living polymerization property drop as compared with polymerization of esters of a tertiary alcohol and methacrylic acid, such as tert-butyl methacrylate.
1,1-Diphenylethylene has no polymerizing ability, and addition reaction of 1,1-diphenylethylene of one molecule with a monovalent anionic compound of one molecule gives an addition reaction product. This addition reaction product has relatively low nucleophilicity and is a stable anionic compound. For this reason, 1,1-diphenylethylene is useful as an anionic modifying agent for alkali metal compounds or a terminal modifying agent for living polymers. As an example of the process (4), there is described an example wherein methyl methacrylate is polymerized, using 1,1-diphenylhexyllithium, which corresponds to an addition reaction product of 1,1-diphenylethylene and n-butyllithium, as a polymerization initiator agent. However, the initiation efficiency thereof is a low value of 0.5 or less.
In order to make anionic polymerization of a methacrylic ester or an acrylic ester suitable for industrial accomplishment, the following are important: living polymerization property is high; initiation efficiency (block efficiency in the case of a block copolymerization) is high; a hydrocarbon based solvent can be used as a solvent media for the polymerization; the scope of polymerization initiator compounds or precursors thereof (organic alkali metal compounds) that can be used is wide; and cooling conditions upon the polymerization can be made mild. Furthermore, a process making it possible to polymerize an ester of a primary alcohol and methacrylic acid or acrylic acid while satisfying these requirements is desired as an industrial production process from the standpoint of highly wide use.
An object of the present invention is to provide a polymerization process making it possible to attain high initiation efficiency (block efficiency in the case of a block copolymerization) and high living polymerization property even when in anionic polymerization of a methacrylic ester or an acrylic ester, an ester of a primary alcohol and methacrylic acid or acrylic acid, which is in general liable to give lowered polymerization results, is used, a compound which is relatively good in safety and handling performance is used as a polymerization initiator compound or a precursor thereof, a hydrocarbon based solvent which can easily be recovered and reused is used as a solvent media for polymerization and a relatively high temperature condition (that is, a relatively mild cooling condition) is adopted as polymerization temperature. According to this polymerization process, it is possible to produce a polymer having a narrow molecular weight distribution and produce a block copolymer containing a small quantity of impurities such as a homopolymer.
Another object of the present invention is to provide a process for producing a polymer with industrial advantage, using the polymerization process having the above-mentioned superior advantages.
The inventors et al. made eager investigations to attain the above-mentioned objects. As a result, it has been found that by conducting anionic polymerization of a methacrylic ester or an acrylic ester in the presence of a specific organoaluminum compound using a specific polymerization initiator compound, it is possible to attain the above-mentioned theme about the application scopes of the methacrylic ester or acrylic ester, the polymerization initiator compound (or the precursor thereof) and the solvent media for polymerization, the above-mentioned theme about the polymerization condition (temperature condition) and the above-mentioned polymerization results (the initiation efficiency and the living polymerization property). The inventor et al. have found that by adding a methacrylic ester or an acrylic ester, as well as a specific organoaluminum compound, to an anionic polymerization system containing a specific polymerization initiator compound, it is also possible to attain the above-mentioned theme about the application scopes of the methacrylic ester or acrylic ester, the polymerization initiator compound (or the precursor thereof) and the solvent media for polymerization, the above-mentioned theme about the polymerization condition (temperature condition) and the above-mentioned polymerization results (the initiation efficiency and the living polymerization property). On the basis of these findings, the inventors have made the present invention.
That is, a first aspect of the present invention is a polymerization process for polymerizing a methacrylic ester or an acrylic ester anionically, using a polymerization initiator compound, wherein an addition reaction product of a conjugated diene compound and an organic alkali metal compound is used as the polymerization initiator compound, and a tertiary organoaluminum compound having in the molecule thereof a chemical structure represented by a formula: Alxe2x80x94Oxe2x80x94Ar wherein Ar represents an aromatic ring is caused to be present in the polymerization system (this polymerization process is referred to as a xe2x80x9cpolymerization process (X)xe2x80x9d hereinafter).
A second aspect of the present invention is a process for producing a polymer, comprising polymerizing a methacrylic ester or an acrylic ester by the polymerization process (X).
A third aspect of the present invention is a polymerization process for polymerizing a methacrylic ester or an acrylic ester anionically, using a polymerization initiator compound, wherein an addition reaction product of a compound having a 1,1-diaryl-1-alkene structure and an organic alkali metal compound is used as the polymerization initiator compound; and the methacrylic ester or the acrylic ester is mixed with a tertiary organoaluminum compound having in the molecule thereof a chemical structure represented by a formula: Alxe2x80x94Oxe2x80x94Ar wherein Ar represents an aromatic ring, and then the resultant mixture is added to the polymerization system (this polymerization process is referred to as a xe2x80x9cpolymerization process (Y)xe2x80x9d hereinafter).
A fourth aspect of the present invention is a process for producing a polymer, comprising polymerizing a methacrylic ester or an acrylic ester by the polymerization process (Y).